Surface plasmon resonance (SPR) based biosensing technology is a useful tool for investigating the binding activity between, for example, cells, proteins, DNA, and small inorganic molecules, and has great potential in biorecognition measurements. SPR based biosensors measure changes in refractive index at a plane interface between two media with dielectric constants of opposite signs, a dielectric and a metal (such as gold).
SPR can be excited when a wedge of polarized light is directed towards the glass face of the sensor surface under the condition of total internal reflection. The resonant angle at which a minimal intensity of reflected light occurs is a function of the local refractive index at or near the metal (such as gold) surface. The changes in refractive index closely associate with the adsorption or desorption of molecules from the surface.
Analysis of biomarker secretion from living cells has useful clinical, medical, and biochemical applications. Biomarker based technology can, for example, provide molecular-based, individualized cancer diagnosis and treatment. Biomarker based cancer therapy can also have reduced side effects when compared to traditional antineoplastic solutions, such as chemotherapy, radiation therapy, and cryosurgery.
Proteomic biomarkers are involved in many types of cancer. Cancer cells rely on vessel growth to provide a constant supply of oxygen and nutrients to maintain tumor growth and cellular activity. Vascular endothelial growth factor (VEGF), which binds to specialized receptors on the surface of endothelial cells, is a widely studied angiogenic signal protein biomarker produced by oxygen-hungry cells to promote the growth of blood vessels. Some types of tumor cells produce abnormally large amounts of VEGF or block the action of angiogenesis inhibitors. This action, termed as “angiogenic switch,” is essential for metastasis of tumor cells.
Existing SPR based sensing platforms can only detect analytes (such as biomarker proteins) in prepared samples, and thus, have certain limitations. For instance, to perform cellular exocytosis and cellular signaling pathways studies, existing SPR based technology usually requires the collection of analytes from cell culture media as well as purification and pretreatment of analytes. These procedures are not only time-consuming, but can also introduce errors into the experiments. Therefore, improved methods for direct measurement of analyte secretion from living cells are needed.